Seal ring for gas turbine

ABSTRACT

A gas turbine blade tip ring seal, which surrounds the blade tips to minimize turbine gas leakage around the blades, that incorporates a thermal protection system that allows modulation of the seal leading edge temperature level and thermal response to minimize seal deterioration during turbine transient operating conditions.

I United States Patent 1 1 3,739,646

Rice et a1. May 1, 1973 [54] SEAL RING FOR GAS TURBINE 3,367,628 2/1968Fittonm, ..415/1 15 2,984,454 5/1961 Fiori ..415/117 [75] Inventors:Alvin S. Rice, South Glastonbury;

Herbert C. Pedersen, Vernon, both FOREIGN PATENTS OR APPLICATIONS ofConn.; Vincent L. Iver-son, Palm Beach Gardens Fla 601,410 1/1960 Italy..4l5/117 [73] Assignee: United Aircraft Corporation, East PrimaryExaminerHenry F. Raduazo Hartford, Conn. Att0rney-Charles A. Warren [22]Filed: June 28, 1971 ABSTRACT [21] Appl' 157515 A gas turbine blade tipring seal, which surrounds the blade tips to minimize turbine gasleakage around the [52] U.S. Cl. ..415/117, 415/172, 415/217 blades,that incorporates a thermal protection system [51] Int. Cl ..'..F01d11/08 that allows modulation of the seal leading edge tem- [58] Field ofSearch ..415/115, 116, 117, perature level and thermal response tominimize seal 415/175, 176, 171, 172, 217; 60/3966 deterioration duringturbine transient operating conditions.

56 R ferences C't d 1 e l e 6 Claims, 2 Drawing Figures UNITED STATESPATENTS 3,451,215 6/1969 Barr ..4l5/1l6 SEAL RING FOR GAS TURBINEBACKGROUND OF THE INVENTION Because of temperature differentials in thegas turbine, a seal that surrounds a row of blades in the turbineparticularly the first stage row of blades is subjected to significanttemperature changes during engine operation and particularly duringtransient conditions. Under steady state conditions, this seal whichregularly extends between the shrouds on adjacent rows of vanes and thusisexposed directly to the hot. turbine gas between the shrouds of onerow of vanes and the adjacent shrouds in the blade has a temperaturedifference between upstream and downstream edges of the seal ring of asmuch as 400F. Under transient conditions this temperature differencebecomes much greater to such an extent that the seal ring is subject toplastic deformation and when it cools, it shrinks to a smaller dimensionthan originally with resultant reduction in the clearance around theblade tips. After several operating cycles the shrinkage is enough tocause damaging rubbing of the seal and blade tip shrouds.

SUMMARY OF THE INVENTION One feature of the invention is an arrangementfor shielding the seal ring to minimize the amount of heat absorbed byradiation from the hot turbine inlet guide vanes and convection from theturbine gas path and also to guide cooling air over the surface of thering thereby keeping the ring cooler particularly at the upstreamportion which is exposed to the highest turbine gas temperature. Anotherfeature is the incorporation of this shield in the turbine structurewith a minimum of engine modification and at the same time obtain thedesired flow of cooling air into the space between the seal ring and theoverlying shield.

In accordance with the invention, a shield is positioned in the. spacebetween the downstream edges of the shrouds in the turbine vanes and thetips of the adjacent turbine blades such that this shield overlies theseal ring in this area in spaced relation thereto. This shield may alsoincorporate an integral ring surrounding the vane shrouds for assistingin directing adequate cooling air into the space between the seal ringand the overlying shield thereby guiding coolingair over the seal ringat its hottest portions.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary longitudinalsectional view through the first stage of the gas turbine.

FIG. 2 is a fragmentary plan view of a portion of the shield.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1 theinvention is shown in connection with the first turbine stage of amulti-stage gas turbine, one example of which is shown in the Savin US.Pat., No. 2,747,367. As shown, the turbine has a casing 2 having aninwardly extending flange 4 which supports the outer shrouds 6 of therow of inlet guide vanes 8 for the turbine. These vanes are hollow andair 1 cooled as will be described. Each shroud has an outwardlyextending flange 10 secured as by bolts 12 to the casing flange 4. Asleeve 14 surrounding the bolts 12 serves to determine the spacing ofthe nuts 16 from the casing flange 4 for a purpose which will appear.

The downstream edges of the shrouds abut against a Z-shaped ring 18which in turn rests against a second flange 20 on the casing 2, thissecond flange being spaced downstream from the first flange. This Z ringextends forwardly in surrounding relation to the row of turbine vanesoutwardly of the shrouds 6 and has an outwardly extending flange 22adjacent the flange 4 and positioned between adjacent bolts 12. Thesecond flange 20 has a plurality of passages 24 therethrough for coolingair.

Downstream of the row of vanes are the cooperating rotating blades 26carried on a disc 28. These blades have tip shrouds 30 thereon which mayhave outwardly projecting fins 32. Cooperating with these shrouds andfins is the surrounding seal ring 34 which extends from a point adjacentto flange 20 downstream beyond the blade shrouds 30 to overlie a thirdflange 36 on the casing. The seal 34 ring and flange 36 have cooperatingloose splines 38 and 40 for locating the seal ring in surroundingrelation to the blades but with a substantial freedom of radial movementto provide for expansion. The seal ring is spaced from flange 20 at itsupstream end to provide a clearance and is surrounded by a spring 42 theconfiguration of which serves to hold the ring in a position to maintainthis clearance. This spring also serves as a vibration damper for theseal ring.

The axial dimension of the seal ring is such that it extends beyond theblade shrouds in both upstream and downstream directions so that thering would regularly be exposed directly to the hot gas passing throughthe turbine. Under these circumstances the seal ring would be exposedupstream of the blade shrouds to the temperature of the gas between thevane shrouds and the blade shrouds, and this gas under steady stateconditions may be 400 hotter than the gas temperature downstream of theblade shrouds to which the downstream portion of the seal ring isexposed. .Under transient conditions this temperature difference will besignificantly greater. These temperature differentials subject the ringto plastic deformation which results in dimensional changes such asshrinkage of the ring with successive operating cycles of the engine.

To minimize these thermal changes, the Z ring 1 which has an inwardlyextending flange 44 engaging against the upstream face of flange 20 alsohas a cylindrical flange or shield 46 extending downstream over the endof flange 20 and into overlying relationship with the upstream portionof seal ring 34. This shield 46 extends a substantial part of thedistance toward the row of blade shrouds 30 preferably almost to theseblade shrouds. This should serve to shield the underlying portion of theseal ring from direct contact with the hot gases in this area and fromradiation from the hot vanes. Cooling air through the passages 24 flowsaround the upstream end of the seal ring and is guided by the shieldover the inner surface of the seal ring. The result is to reduce thetemperature differentials in the seal ring to such an amount as toreduce the seal ring shrinkage to about one-tenth of the previousshrinkage.

The cooling air used is obtained from around the flame tubes and isreferred to as secondary combustion air. This air is in the space 48upstream of casing flange 4 and passes between flange 22 and flange 4into the space 50 between casing flanges 4 and and outside of Z ring 18.This cooling air then flows through passages 24 into space .52downstream of flange 20 and around the upstream end of the seal ring 34as above described. Some of the cooling air in space 48 also enters thespace 54 radially inward of the Z ring 18 and enters the vanes 8 forcooling them. Some of this cooling air also flows inwardly betweenadjacent shrouds 6 to flow over and cool the inner surface of theseshrouds and also over the inner surface of the shield for cooling thisto some extent.

The Z ring 18 is preferably slotted to minimize thermal distortion. Asshown in FIG. 2, deep slots 56 extend forwardly from the downstream edgeof shield 46 to include flange 44 and into the main portion of the Zring. The forward end of the Z'ring is also preferably notched as at 58and these notches also extend into the main portion of the Z ring. Thesenotches are relatively wide and provide passages for the flow of coolingair from space 48 into the space 54 as above described.

We claim:

1. The combination with a row of turbine vanes having outer shrouds, acasing surrounding the outer shrouds and supporting said row of vanes, arow of turbine blades downstream of and adjacent to said varies and acontinuous seal ring extending around the tips of the blades in closeproximity thereto and supported within said casing, said seal ring alsoprojecting forwardly of the tips of the blades, of a shield extendingdownstream of and separate from the shrouds and substantially inalignment therewith and overlying at least a part of the seal ring forshielding said ring from the hot gases passing over the van'es andblades.

2. The combination as in claim 1 in whichthe shield extendssubstantially to the blade tips;

3. The combination as in claim 1 in which means are provided fordischarging cooling air into the space between the seal ring and theshield.

4. The combination as in claim 1 in which the seal ring extends upstreamsubstantially to the shrouds and the shield overlies this portion ofring and extends substantially to the tips of the blades. 4

5. The combination with a row of turbine vanes having outer shrouds, arow of turbine blades downstream of and adjacent to said varies, acasing surrounding said vanes and blades and supporting said vanes, anda continuous seal ring extending around the tips of the blades in closeproximity thereto and also projecting forwardly of the tips of theblades substantially to the vane shrouds, said seal ring being supportedby the casing for radial movement relative thereto, of a shieldextending downstream of and separate from the shrouds and substantiallyin alignment therewith and overlying the portion of the seal ringbetween the vaneshrouds and blade tips for shielding said ring.

6. The combination as in claim 5 in which the casing has an inwardlyextending flange for supporting the shield, said flange having meanstherein for directing cooling fluid to the outer surface of the upstreamend of the seal ring.

' a: is

1. The combination with a row of turbine vanes having outer shrouds, acasing surrounding the outer shrouds and supporting said row of vanes, arow of turbine blades downstream of and adjacent to said vanes and acontinuous seal ring extending around the tips of the blades in closeproximity thereto and supported within said casing, said seal ring alsoprojecting forwardly of the tips of the blades, of a shield extendingdownstream of and separate from the shrouds and substantially inalignment therewith and overlying at least a part of the seal ring forshielding said ring from the hot gases passing over the vanes andblades.
 2. The combination as in claim 1 in which the shield extendssubstantially to the blade tips.
 3. The combination as in claim 1 inwhich means are provided for discharging cooling air into the spacebetween the seal ring and the shield.
 4. The combination as in claim 1in which the seal ring extends upstream substantially to the shrouds andthe shield overlies this portion of ring and extends substantially tothe tips of the blades.
 5. The combination with a row of turbine vaneshaving outer shrouds, a row of turbine blades downstream of and adjacentto said vanes, a casing surrounding said vanes and blades and supportingsaid vanes, and a continuous seal ring extending around the tips of theblades in close proximity thereto and also projecting forwardly of thetips of the blades substantially to the vane shrouds, said seal ringbeing supported by the casing for radial movement relative thereto, of ashield extending downstream of and separate from the shrouds andsubstantially in alignment therewith and overlying the portion of theseal ring between the vane shrouds and blade tips for shielding saidring.
 6. The combination as in claim 5 in which the casing has aninwardly extending flange for supporting the shield, said flange havingmeans therein for directing cooling fluid to the outer surface of theupstream end of the seal ring.